Wonderwall

There's no house party like a White House party! On the evening of Monday Jan. 21 -- following more public, official inauguration galas -- President Barack Obama and First Lady Michelle Obama opened up their historic Washington, D.C. home to about 400 super-VIP guests for a private shindig.

Mr. and Mrs. Obama arrived for the festivities around 10 p.m. alongside daughters Malia, 14, and Sasha, 11. Once it was time for DJ Cassidy to spin some tunes, the floor was cleared for dancing -- and live performances from the likes of Eric Benet, Janelle Monae and Ledisi. During Cassidy's DJ set, Usher, Perry, Keys and Hudson each took the floor to sing along to their hits.

"The party went on until 2 a.m.!" the source marvels to Us, adding that the President and his family all hit the dance floor. "They all stayed until the end… Obama was dancing with everyone and let his guard down!"

"Teenage Dream" singer Perry, 28, tweeted about the unforgettable bash. "Just left the White House. All other parties from here on out will be judged unless they take place at the White House."

"Just partied at the White House," added Clarkson, who sang "My Country Tis of Thee" during the inauguration ceremony earlier in the day. "I kid you not, Michelle Obama stood up and got the party started ....seriously cool First Lady."